Biology Books
Biology - Onion Cell Lab Notes

Video: Onion Cell Lab

Video: Osmosis

Animal Cell

-	cell membrane allows material to pass easily into and out of the cell
-	flexible
-	small vesicles for transport
-	small vacuoles for storage
-	centrioles function in cell respiration
-	lysosomes contain digestive material

Plant Cell

-	cell wall provides protection and support
-	large vesicles for storage
-	large vacuoles for storage
-	chloroplasts have chlorophyll; important for photosynthesis
-	leucoplasts for making and storing starch

Cell Physiology

Physiology has to do with biological functions in physical 
operations. Cells have a steady state or homeostasis. 
Homeostasis is the process of maintaining a constant internal 
environment, despite changing in external conditions.  Substances 
must enter and leave constantly in the cell through the cell 
membrane, in order for this balance to occur.  The membrane is 
selectively permeable, meaning some materials are admitted and 
some are not.

Whether or not particles pass through this membrane depends on:
a)	size of the particle
b)	size of the opening (structure of the membrane)
c)	chemicals making up the particle
d)	whether or not the particle dissolves in water

Remember: All particles of all substances are in 
                 constant Brownian Movement.

Diffusion: Movement of particles from a greater 
concentration to an area of lower concentration, until 
there is an equal concentration of particles eg., a drop of 
ink in a glass of water.  Movement occurs naturally, 
simply because the molecules are in motion. No energy is required.

Osmosis is a special kind of diffusion.  It is simply 
the movement of water from an area where there is lots to an
area where there is little.  Animal cells can burst is they
don't get rid of this extra water, and die.  They have no cell walls.  
Therefore, the amount of water must be controlled.

Water Concentration:

Isotonic - water concentration inside the cell equals that outside   
                Red blood cell remains unchanged.
                Plant cell remains unchanged.

Hypotonic - greater concentration of water outside the cell
                    Red blood cell bursts as water enters.
                    Plant cell swells as water enters.
                    Onion cell swells in fresh water.

Hypertonic - greater concentration or water inside of cell 
                      Red blood cell shrinks.
                      Plant cell contents shrink.  
                      Contents of an onion cell in salt water shrink.